1. Field of the Invention
The present invention relates a thermal insulator and, more particularly, to a thermal insulator provided to a heat treatment apparatus used for a semiconductor manufacturing apparatus and a heat recycle system using such a thermal insulator.
2. Description of the Related Art
Since a temperature of a heat treatment furnace, which applies a heat treatment to a semiconductor wafer, becomes very high, a thermal insulator is provided around the heat treatment furnace. That is, heat released from an electric heater for heating the heat treatment furnace is shielded by the thermal insulator so as to prevent the heat from leaking outside of the heat treatment furnace.
Conventionally, such kind of thermal insulator is formed of so-called ceramics wool. The ceramics wool is made of fine fibers of minerals, and the ceramics wool is provided around the heat treatment furnace in the form of a fabric or a board. The thermal insulation of the ceramics wool is achieved by a very low thermal conductivity of minerals, which are materials of the ceramics wool, and tiny spaces formed between the fibers.
Japanese Laid-Open Patent Application NO. 60-80077 discloses a method of insulating a furnace by constituting outer walls of the furnace using a heat insulation member having a honeycomb structure. In this method, an airflow passage is formed by internal spaces of the honeycomb structure member. The furnace is insulated and cooled by passing a cooling air through the airflow passage. Moreover, it is suggested to collect the air used for cooling and store the heat of the air in a thermal storage apparatus or use the collected high-temperature as a combustion air for the furnace.
A heat treatment apparatus of a semiconductor manufacturing apparatus has a structure in which a heat treatment furnace and a conveyance mechanism for conveying semiconductor wafers are provided inside a housing. Therefore, when a heat-treated semiconductor wafers are taken out of the heat treatment furnace, the housing of the heat treatment apparatus is heated. For example, if a heat treatment temperature of the semiconductor wafers is 1000xc2x0 C., the semiconductor wafers after the heat treatment will be taken out of the heat treatment furnace at a temperature of about 800xc2x0 C. Therefore, the housing of the heat treatment apparatus is heated by the hot air exhausted from the heat treatment furnace together with the semiconductor wafers. Moreover, the housing is partially heated by the radiation heat of the semiconductor wafers taken out of the furnace.
As mentioned above, the thermal insulator, which insulates the circumference of the heat treatment furnace of the heat treatment apparatus, is formed of a material such as ceramics wool, and if the heat treatment furnace is covered by the thermal insulator having a uniform thickness, any portion of the heat treatment furnace will be provided with uniform heat insulation efficiency. A vertical furnace, which is widely used from among heat treatment furnaces, has a vertical length as long as more than 1 meter. If such a vertical furnace is uniformly heated in the vertical direction by an electric heater, variation in the temperature may occur in the vertical direction of the furnace. That is, since the heated air moves upward within the vertical furnace, a temperature of an upper portion becomes higher than a temperature of a lower portion of the vertical furnace. In order to apply a uniform heat treatment to the semiconductor wafers provided in the vertical furnace, such a variation in the temperature must be eliminated as much as possible.
Then, in a conventional vertical furnace, a power supplied to the electric heater is controlled so that an amount of heat generated by the electric heater in an upper portion of the vertical furnace is larger than an amount of heat generated in a lower portion of the furnace. That is, the power supplied to the electric heater is increased toward a bottom of the vertical furnace. Generally, an electric heater is located in the vicinity of an inner wall of an insulator, which surrounds the vertical furnace. If the thickness of the insulator is uniform, that is, if the insulation efficiency of the insulator is uniform, there is a problem in that the heat of a lower portion of the vertical furnace passing through the insulator and released to the atmosphere is larger than the heat of an upper portion of the vertical furnace passing through the insulator and released to the atmosphere.
In the conventional thermal insulator using ceramics wool, in order to change the heat insulation characteristic, only a control, which merely changes a thickness of the thermal insulator, can be performed and a fine control cannot be achieved. On the other hand, the heat insulation characteristic of the honeycomb structure thermal insulator disclosed in the above-mentioned Japanese Laid-Open Patent Application No. 60-80077 can be changed by controlling a quantity of air flowing through inside of the thermal insulator. However, the heat insulation characteristic can be merely changed with respect to the entire honeycomb structure thermal insulator, and the heat insulation characteristic cannot be changed partially.
Moreover, in the thermal insulator using ceramics wool, a heat treatment furnace cannot be cooled forcibly. Therefore, in order to lower the temperature of the furnace after completion of a heat treatment so as to take out semiconductor wafers from the furnace, it cannot but depend only on cooling by exhausting air in the heat treatment apparatus. For example, in order to lower the temperature of a 1000xc2x0 C. semiconductor wafer to 800xc2x0 C., the semiconductor wafer after the heat treatment must be remain inside the heat treatment furnace for a long time. Therefore, there is a problem in that the heat treatment process time of a semiconductor wafer is long.
Moreover, generally a housing of a heat treatment apparatus is formed with a steel plate or the like. If a high-temperature semiconductor wafer is taken out of a vertical furnace within a heat treatment apparatus, a portion of a housing near the semiconductor wafer is heated by radiation. Thus, the heat in the heat treatment apparatus is released to a clean room through the housing, thereby increasing a temperature inside the clean room. For this reason, a load is applied to the air-conditioner for maintaining the clean room air at a constant temperature, and a running cost of the clean room increases. Therefore, in order to prevent a heat generated within a heat treatment apparatus from being released to the clean room through the housing, the housing itself is formed by a thermal insulator and heat insulation efficiency is increased partially.
It is a general object of the present invention to provide an improved and useful thermal insulator in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide a thermal insulator which can change a heat insulation characteristic partially with a simple structure.
Another object of the present invention is to provide a thermal insulator which can be cooled per se while insulating a heat source.
A further object of the present invention is to provide a thermal insulator which allows recycle of heat collected by cooling the thermal insulator, and a heat recycle system using such a thermal insulator.
In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention a honeycomb structure thermal insulator for intercepting a heat released from a heat source, comprising: a plurality of parts defined by dividing the honeycomb structure thermal insulator in accordance with a temperature of the heat source, the plurality of parts being formed of different honeycomb structures, respectively, so as to provide different heat insulation characteristics.
In the honeycomb structure thermal insulator according to the present invention, the plurality of parts may be formed of different materials. Additionally, each of the materials of the honeycomb structures may contain a mixture of alumina fiber and silica fiber so that the materials are formed in different compositions by varying a mixing ratio of the alumina fiber and the silica fiber. Further, the plurality of parts may be provided with different heat insulation characteristics by varying a weight per unit volume of the honeycomb structure. The weight per unit volume of the honeycomb structure may be varied by changing a cell pitch of the honeycomb structure.
The honeycomb structure thermal insulator according to the present invention may further comprise air supply means for supplying air to the honeycomb structure so that each cell of the honeycomb structure serves as an air passage. Additionally, the honeycomb structure thermal insulator may further comprise a coolant passage through which a coolant flows so as to cool the air flowing trough the air passage defined by each cell.
When the heat source is an electric heater provided around a vertical heat treatment furnace, the honeycomb structure thermal insulator may have a cylindrical shape so as to substantially enclose the electric heater and the honeycomb structure thermal insulator may be divided into the plurality of parts in a radial direction of the honeycomb structure thermal insulator.
When the heat source is an electric heater provided around a vertical heat treatment furnace, the honeycomb structure thermal insulator may have a cylindrical shape so as to substantially enclose the electric heater and the honeycomb structure thermal insulator may be divided into the plurality of parts in a vertical direction of the honeycomb structure thermal insulator. Additionally, the plurality of parts may be defined by dividing the honeycomb structure thermal insulator in accordance with heat control zones of the electric heater.
Additionally, there is provided according to another aspect of the present invention a honeycomb structure thermal insulator for intercepting heat released from a heat source, comprising: a plurality of cells constituting a honeycomb structure; and a coolant passage through which a coolant flows so as to cool air in the cells.
Further, there is provided according to another aspect of the present invention a heat recycle system for reusing heat collected by a thermal insulator, the heat recycle system comprising: a honeycomb structure thermal insulator for insulating a heat treatment furnace of a heat treatment apparatus; heat collecting means for collecting heat from inside the honeycomb structure thermal insulator; heat transfer means for transferring the collected heat to a predetermined part; and heating means for heating the predetermined part by the heat transferred by the heat transfer means.
In the heat recycle system according to the present invention, the heat collecting means may include a coolant passage through which a coolant flows so as to cool air inside the honeycomb structure thermal insulator, and the heat transfer means may include a coolant supply passage for transferring the coolant discharged from the coolant passage to the predetermined part.
The predetermined part may be a manifold provided to the heat treatment furnace. Also, the predetermined part may be an external combustion apparatus connected to a manifold provided to the heat treatment furnace. The predetermined part may be a material gas supply passage for supplying a material gas to a manifold connected to the heat treatment furnace. The predetermined part may be an exhaust passage for exhausting an exhaust gas from a manifold connected to the heat treatment furnace.
As mentioned above, according to the present invention, a thermal insulator of which heat insulation characteristic can be changed partially with a simple structure by using a honeycomb structure as the thermal insulator. Additionally, according to the present invention, the thermal insulator itself can be cooled while insulating a heat source by the honeycomb structure thermal insulator, and, heat can be collected from the honeycomb structure thermal insulator and reused as a heat source for other parts.
Other objects, features and advantages of the present invention will become more apparent from the following detailed descriptions when read in conjunction with the accompanying drawings.